This application claims the benefit of Korean Patent Application No. p98-44179, filed on Oct. 21, 1998, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to an apparatus and a technique for driving a liquid crystal panel in a liquid crystal display device, and more particularly to a driving method of driving a liquid crystal panel in an inversion system and an apparatus thereof.
2. Description of the Prior Art
Generally, a liquid crystal display device controls the light transmissivity of liquid crystal cells in a liquid crystal panel to display a picture corresponding to a video signal. Such a liquid crystal display device uses generally four driving methods, such as line inversion system, column inversion system, dot inversion system and group inversion system, so as to drive the liquid crystal cells in the liquid crystal panel.
In a liquid crystal panel driving method of line inversion system, as shown in FIG. 1A and FIG. 1B, polarities of data signals applied to the liquid crystal panel are inverted in accordance with row lines, e.g., gate lines, on the liquid crystal panel in each frame. In a liquid crystal panel driving method of column inversion system, as shown in FIG. 2A and FIG. 2B, polarities of data signals applied to the liquid crystal panel are inverted in accordance with column lines, e.g., source lines, on the liquid crystal panel in each frame. A cross talk in a vertical direction seriously emerges in a picture displayed on the liquid crystal panel by means of the liquid crystal panel driving method of column inversion system. In other words, the liquid crystal panel driving method of column inversion allows a serious flicker to emerge between vertical lines.
In a liquid crystal panel driving method of dot inversion system, as shown in FIG. 3A and FIG. 3B, data signals having polarities contrary to the adjacent liquid crystal cells on the gate lines and to the adjacent liquid crystal cells on the data lines are applied to each liquid crystal cell in the liquid crystal panel, and the polarities of data signals applied to all liquid crystal cells in the liquid crystal panel are inverted every frame. In other words, in the dot inversion system, data signals are applied to the liquid crystal cells in the liquid crystal panel in such a manner that the positive (+) polarity and the negative (xe2x88x92) polarity appear alternately as shown in FIG. 3A as it goes from the liquid crystal cell at the left upper end into the liquid crystal cells at the right side and into the liquid crystal cells at the lower side when a video signal in the odd numbered frame is displayed; while data signals are applied to the liquid crystal cells in the liquid crystal panel in such a manner that the positive (+) polarity and the negative (xe2x88x92) polarity appear alternately as shown in FIG. 3B as it goes from the liquid crystal cell at the left upper end into the liquid crystal cells at the right side and into the liquid crystal cells at the lower side when a video signal in the even-numbered frame is displayed.
Finally, in a liquid crystal panel driving method of group inversion system, assuming that liquid crystal cells in the liquid crystal panel are divided into liquid crystal groups having a certain number (e.g., 2) of liquid crystal cells each, as shown in FIG. 4A and FIG. 4B, data signals having polarities contrary to the adjacent liquid crystal cell groups on the gate lines and to the adjacent liquid crystal cell groups on the data lines are applied to each liquid crystal group. Also, the liquid crystal panel driving method of group inversion system allows the polarities of data signals applied to all liquid crystal cells in the liquid crystal panel to be inverted every frame.
A picture displayed on the liquid crystal panel according to the liquid crystal panel driving method of line inversion system in these liquid crystal panel driving methods has a serious cross talk in the vertical direction. Particularly, when a picture alternates between two colors, for example, a color with a medium gray scale and a black color, and is displayed on the liquid crystal panel by the liquid crystal panel driving method of line inversion system as shown in FIG. 5, a serious flicker emerges between the horizontal lines depending on the line.
On the other hand, a picture displayed on the liquid crystal panel according to the liquid crystal panel driving method of column inversion system has a serious cross talk in the horizontal direction. Further, when a picture alternates between two colors, for example, a color with a medium gray scale and a black color, depending on the column lines by the liquid crystal panel driving method of line inversion system is displayed on the liquid crystal panel, a serious flicker emerges between the horizontal lines. On the other hand, the liquid crystal panel driving methods of dot and group inversion system having the polarities of data signals inverted in both the vertical and horizontal direction provide more excellent quality of pictures compared with the line and column inversion systems. Owing to this advantage, the liquid crystal panel driving methods of dot and group inversion system have been widely used in the industry.
However, the liquid crystal panel driving methods of dot and group inversion system reveal a frame inversion effect when a specific pattern, such as check pattern, subpixel pattern and windows shut-down mode pattern, etc., is displayed. Due to this, a flicker is generated and, further, the picture quality deteriorates in a picture displayed by the liquid crystal panel driving methods of dot and group inversion system. More specifically, only liquid crystal cells indicated with oblique lines and liquid crystal cells indicated with oblique lines when a potential difference between data signals applied to the remaining cells is large in liquid crystal cells on the liquid crystal panel shown in FIG. 7 and FIG. 8 are assumed to be driven in a pattern having the polarities inverted every frame. In other words, only liquid crystal cells indicated with the oblique lines in FIG. 7 and FIG. 8 seem to be driven with the frame inversion system. Due to this, in the liquid crystal panel driving methods of dot and group inversion system, a flicker noise emerges on the screen is dictated by a picture pattern. As a result, picture quality displayed by the liquid crystal panel driving methods of dot and group inversion system is inconsistent.
Accordingly, it is an object of the present invention to provide a liquid crystal panel driving method and apparatus that is adaptive for keeping the picture quality independently of a picture pattern as well as improving the picture quality.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In order to achieve these and other objects of the invention, a liquid crystal panel driving apparatus comprises a liquid crystal panel having liquid crystal cells arranged in a substantially matrix form; drivers arranged adjacent the liquid crystal cells to drive each one of the liquid crystal cells; a frequency controller responsive to a first input signal and a first clock signal to output at least two polarity control signals; and a multiplexor connected to the frequency controller to selectively output one of at least two polarity control signals to the drivers to control polarity of liquid crystal cells.
According to one aspect of the present invention, the frequency controller includes a first frequency divider responsive to a first input signal and a first clock signal to provide a first output; a second frequency divider responsive to the first output and the first clock signal to provide a second output; and a third frequency divider responsive to the second output and the first clock signal to provide a third output. The first, second and third outputs are frequency divided signal of the first input signal. The frequency controller further includes a counter responsive to a first clock signal to output a count signal to control the multiplexor. In the preferred embodiment of the present invention, the multiplexor is responsive to the count signal from the counter to output one of the at least two polarity signals to the drivers. In particular, the multiplexor is responsive to the count signal from the counter to output one of the first, second and third outputs from the first, second and third frequency dividers, respectively, to the drivers.
According to another aspect of the present invention, the first, second and third frequency dividers are flip-flops. In addition, the counter is preferably of a modulo 4 type. In the present invention, the first input signal is a horizontal sync signal and the first clock signal is a vertical sync signal.
According to the present invention, a method of driving a liquid crystal panel having liquid crystal cells comprises the steps of (a) grouping the liquid crystal cells in the liquid crystal panel into a plurality of polarity blocks, each polarity block having an initial number of liquid crystal cell; (b) applying data signals having a first polarity to liquid crystal cells in a first polarity block during a first frame; (c) applying data signals having a second polarity to liquid crystal cells in a second polarity block located adjacent the first polarity block during a second frame; and (d) incrementing a number of liquid crystal cells in the first and second polarity blocks by at least one liquid crystal cell. The steps of (b) to (d) are repeated in subsequent frames.
According to one aspect of the present invention, the liquid crystal cells of the first and second polarity blocks are arranged in a first direction of the liquid crystal panel. In particular, the first direction constitutes a vertical direction of the liquid crystal panel.
After repeating the steps of (b) to (d) for at least three times, the number of liquid crystal cells in the first and second polarity blocks are reset to the initial number of liquid crystal cell.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.